Method of fabricating a system-on-panel typed liquid crystal display

ABSTRACT

A system-on-panel typed liquid crystal display has active layers of single crystalline silicon for fabricating such high speed circuits as drivers, controllers, and central process units. By forming such active layer on a common substrate, the high speed circuits can coexist with lower speed pixel array. As a result, the system-on-panel LCD enables the efficient fabrication of a pixel array, a driver, a controller and a CPU circuit on the same substrate, whereby the fabrication process is simplified and production yields are increased. Moreover, the present invention facilitates the fabrication and manufacture of portable LCD products which are significantly reduced in weight and size because the space occupied by the controller and the CPU circuit is markedly and desirably reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system-on-panel typed liquid crystaldisplay, and more particularly, a system-on-panel including activelayers of single crystalline silicon for use with a driver, acontroller, and a central processing unit.

2. Description of the Related Art

Liquid crystal display (hereinafter LCD) panels are flat-panel displayswhich are used in a variety of products, including consumer electronics,computers, and communication terminals.

When liquid crystal displays are used, a subsystem comprising thedrivers for driving the data and the gate lines, a controller forcontrolling the LCD, and a central processing unit (hereinafter CPU)circuit for controlling the controller and performing the arithmetic andlogic processes, is generally required. The controller and the CPUcircuit are often comprised of a CPU, ROMs, RAMs, oscillators andresistors.

The structure of an LCD display panel is a simple one. The liquidcrystal is encapsulated between two glass substrates, a TFT substrate,and a color-filter/common electrode substrate. That is, the TFT and thecolor-filter/common electrode substrates are two parallel sheets ofglass with liquid crystal injected between them.

More specifically, LCD panels may include: (1) a lower plate on which aplurality of unit cells comprised of switching devices, such as TFTs andpicture elements (hereinafter pixels) are arranged; (2) an upper platecomprising color filters, also called the common electrode substrate;(3) liquid crystal injected between these two plates; (4) a polarizingplate which polarizes visible light between the plates; and (5) abacklight for supplying light from one of the plates.

The transparent common electrode on the upper plate/substrate can bemade of ITO (Indium Tin Oxide), and is deposited on top of the colorfilter substrate. In order to obtain good display quality, the cell gapof the liquid-crystal (i.e., the spacing between the two glasssubstrates) has to be precisely controlled to a specific value. This gaphas to be uniform over the whole display area and reproducible from oneend to the other. Therefore, transparent spacers, such as plastic beads,are placed on the surface of the glass substrates.

Furthermore, a transparent insulating glass substrate that is perviousto light, is used. Normally, two layers of insulators are formed on agate electrode. Insulating substrates are used because when lightstrikes the semiconductor layer, the resulting photoelectric conversionproduces a current, thus increasing the amount of off-current. This cancause malfunction in the case of LCD panels. To prevent this problem,the semiconductor layer is completely shielded from light. Anotherreason for using insulating substrates is for protection of thesemiconductor layer during the manufacturing process of other layerssuch as when drain and source electrodes are formed so that thesemiconductor is protected from structural and physical damage.

LCD panels are manufactured under low temperature conditions in order toprotect the glass substrates from damage because glass has a relativelylarge specific gravity and is weakened and brittle when heated.

FIGS. 1A-1C show various types of LCDs. In FIG. 1A, an LCD according toa first related art which uses amorphous silicon thin film transistor(hereinafter TFT) deposited on a glass substrate 100 as the switchingdevice of choice for the pixel array shown.

However, in this situation, the driver in an LCD is required to performvery fast switching operations. Forming the switches using amorphoussilicon TFTs is not an appropriate method in order to achieve quickswitching operations in an efficient manner. Instead, the use of siliconchips formed by fabricating metal oxide silicon transistors (hereinafterMOS transistors) on silicon wafers attached to a glass substrate 100where pixels for the LCD have been formed is more desirable.Subsequently, the controller for controlling the drivers and the CPUcircuit may be provided by a separate phase of the manufacturingprocess.

As illustrated in FIG. 1B, a new technique of forming polycrystallinesilicon (hereinafter p-Si) under low temperature conditions has beendeveloped. Polycrystalline silicon TFTs are easily fabricated on glasssubstrates using a number of manufacturing techniques. One of suchtechniques proposed involves laser crystallization for formingpolycrystalline silicon by depositing amorphous silicon on a glasssubstrate under low temperature conditions and, successively, byscanning the amorphous silicon with a laser beam.

The above-proposed technique enables fabrication of an LCD having abuilt-in driver because the pixel array comprising the TFT switches andthe drivers are directly formed on the glass substrate 100.Unfortunately, a controller made of single crystalline silicon and a CPUcircuit are provided by separate processes and on a separate substrate.

In FIG. 1C, another technique for manufacturing a system-on-panel(hereinafter SOP) is shown. This technique enables fabrication of an LCDby mounting a CPU circuit and a controller, comprised of a CPU, ROMs,RAMS, and oscillators on a glass substrate. Accordingly, by formingpixels as an image display and a driver on the glass substrate 100 andmounting a controller, and a CPU circuit to control the pixels on theglass substrate 100, it is possible to fabricate a portable LCD productwhich is significantly improved in terms of reduced weight and size.

FIG. 2 shows a cross-sectional view of an SOP typed LCD according to aJapanese Publication No. 8-313935. In this cross-sectional illustration,an aluminum layer 2 having patterns corresponding to drain/source wiresand contact wires of a CPU circuit oriented in the y-direction isdeposited on a glass substrate 1 by sputtering. Next, a polycrystallinesilicon layer 3 for a source/drain region is formed by Low PressureChemical Vapor Deposition (hereinafter LPCVD). A P+ layer or an N+ layeris formed by doping the p-Si layer 4 with impurity ions, such as boron(B) or phosphorus (P). Another p-Si layer 4 of an active layer is formedon the P+ or the N+ layer by LPCVD. After the p-Si layer 4 has beenactivated by thermal treatment, a gate insulating silicon oxide layer 5is formed.

Thereafter, the following layers are formed successively: (1) analuminum (hereinafter Al) layer 6 comprising the gate electrodes; (2) anAl wire 7 oriented in the y-direction; (3) a mounting pad 8 for a CPU,RAM, ROM, and IC; (4) a lead attachment pad 9; and (5) a bare-chipmounting pad 8 for the resistors, capacitors, oscillators andconnectors.

A color filter substrate/common electrode 15 having an ITO layer 16interposed thereon is formed on an opposite substrate 17. Glasssubstrate 1 manufactured by the above-described steps is assembled withthe opposite substrate 17. The liquid crystal 14 is injected between thecolor filter substrate/common electrode 15 and the opposite substrate17. The subcomponents of the LCD panel or module, that is, theperipherals such as the CPU, RAM, ROM, IC, resistors, capacitors,oscillators, connectors and the like, found on the bare chip 11, arefixed to the mounting pad 8. Wires 10 are connected to each successivechip in a process of molding involving resin 12. Finally, polarizingplates 13 and 18 which either transmits or absorbs a specific componentof polarized light 13 and 18 are provided.

In the related art described above, after forming the CPU circuit andthe controller by a separate semiconductor process, on a wafer of singlecrystalline silicon, the CPU circuit and the controller consisting of aCPU, RAM, ROM, IC, resistors, capacitors, oscillators, connectors, areattached to a panel of the LCD in order to fabricate an SOP typed LCD.

In the prior art techniques discussed so far, each integrated circuit ICchip (hereinafter IC chip) in a controller and a CPU circuit isfabricated on a silicon wafer by a general semiconductor fabricationprocess and then subsequently attached to a glass substrate since thecontroller and the CPU circuit are formed with single crystallinesilicon. Accordingly, the process of fabricating pixels and LCD driversare kept separate from other processes for fabricating the controllerand the CPU circuit. The SOP typed LCD manufactured by the foregoingtechnique reaches the limits of lightness and product miniaturizationsince the controller and CPU circuit occupy a certain space.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay of system on panel that substantially obviates one or more ofthe problems due to limitations and disadvantages of the related art.

The object of the present invention is to provide an SOP typed LCDfabricated by forming all of the required subcomponents of the LCD panelor module on one substrate, namely, a controller, a CPU circuit, thepixel array, and drivers of the LCD panel.

Another object of the present invention is to provide an SOP typed LCDcomprising the pixels of the LCD, a driver, a controller and a CPUcircuit on a substrate by fabricating the controller and CPU circuit ona glass substrate by using the technique of forming single crystallinesilicon on an insulated glass substrate.

Additional features and advantages of the invention will be set forth inthe description which follows and will be apparent from the figuresprovided and the detailed description, or may be learned by practicingof the invention.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the presentinvention includes a pixel part, a driver, a controller and a CPUcircuit wherein the controller and the CPU circuit further includedevices which are comprised of active layers of single crystallinesilicon.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the inventing andtogether with the description serve to explain the principle of theinvention.

FIGS. 1A-1C show various types of LCD;

FIG. 2 shows a cross-sectional view of an SOP typed LCD according to arelated art;

FIG. 3A-3C illustrate the method for crystallizing an amorphous siliconfilm by Sequential Lateral Solidification (SLS) technique;

FIG. 4A-4B show cross-sectional drawings along the line I-I and II-II asshown in FIG. 3C.

FIG. 5 shows a cross-sectional view of an SOP typed LCD according to anembodiment of the present invention; and

FIG. 6 shows a schematic cross-sectional view of a first substrate ofthe SOP typed LCD as shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiment of thepresent invention, an example of which is illustrated in theaccompanying drawings.

The present invention provides an SOP typed LCD fabricated by formingall of the required subcomponents, such as a controller, a CPU circuit,and both pixels and a driver of an LCD panel on a substrate.Particularly, an SOP typed LCD is manufactured by fabricating pixels ofthe LCD, a driver, a controller and a CPU circuit simultaneously onpreferably a transparent insulated glass substrate.

As mentioned above, a controller and CPU circuit including a CPU, ROM,RAM must be made of single crystalline silicon in order to be operatedunder a high frequency. A prior art technique for fabricating an SOPtyped LCD includes the steps of separately forming a chip on a wafer ofsingle crystalline silicon by a semiconductor fabrication process andthe step of attaching the chip to an LCD substrate. The controller andthe CPU circuit of the SOP typed LCD are fabricated by a separateprocess in prior art methods because it is very difficult to form singlecrystalline silicon on a glass substrate.

However, if fabrication of a built-in SOP typed LCD in which acontroller and a CPU circuit are formed on the glass substrate ispossible, then this new technique for forming single crystalline siliconon a glass substrate enables the fabrication of the controller and theCPU circuit of the SOP typed LCD in the same process as the fabricationof the semiconductor and LCD substrate.

There are several techniques for forming single crystalline silicon on aglass substrate. Sequential Lateral Solidification is one technique thatforms the silicon layer, by applying laser to an amorphous siliconlayer. Here, the displacement of the laser beam is shorter than thelength of lateral growth of the crystal. Consequently, silicon particleswhich are longer than 10 μm are formed on a glass substrate. Theforegoing technique is disclosed in “Crystalline Si Films For IntegratedActive Matrix Liquid-Crystal Displays,” MRS Bulletin, Volume XXI, Number3, March 1996, pp. 39˜48.

Moreover, the location, size, and shape of a crystal particle may becontrolled by manipulating the shape of a slit through which a laserbeam passes, which enables the formation of silicon particles that arelarger than an active area of a TFT. Thus, it is possible to fabricate aTFT of single crystalline silicon manufactured by forming an active areaof the TFT as a single crystal particle.

FIGS. 3A-3C show the method for crystallizing an amorphous silicon filmby the Sequential Lateral Solidification (SLS) technique. The techniqueof forming a single crystalline silicon layer on a glass substrate bySLS is well-known in the art, as is described in “Single Crystal SiFilms Via A Low-Substrate-Temperature Excimer-Laser CrystallizationMethod,”

by Robert S. Sposilli, M. A. Crowder, and James S. Im, Mat. Res. Soc.Symp. Proc., Vol. 452, pp. 956-7, 1997.

The SLS technique used in the present invention relies on the fact thatsilicon grains tend to grow vertically against the interface betweenliquid and solid silicon, and that an amorphous silicon layer iscrystallized by controlling the magnitude of laser energy andirradiation range of a moving laser beam in order to maintain the growthof silicon grains laterally for a predetermined length. This phenomenonis embodied in the present invention.

As seen in FIG. 3A, the narrow region having a straight slit film shapebounded by the dashed lines is the first irradiated region. This firstirradiated region is irradiated at an energy density sufficient toinduce complete melting. Subsequently, lateral grain growth proceedsfrom the unmelted regions adjacent to the narrow strip which has beenfully melted. The grain boundaries in the directionally solidifiedmaterials tend to form in order to be maintained perpendicularly to themelting interface. Depending on the width of the molten region, lateralgrowth ceases to occur with either of two situations: (1) the twoopposing growth fronts collide at the center, or (2) the molten regionbecomes sufficiently supercooled so that bulk nucleation of solidsoccur, whichever occurs first. Because of such considerations, themaximum lateral growth distance which can be achieved with asingle-pulse is limited to less than certain length, depending on thefilm thickness and the incident energy density.

In FIG. 3B, the film is translated relative to the beam image over adistance of less than the single-pulse lateral growth distance, and thenirradiated again. As lateral growth begins again from the edges of thecompletely molten region located within the grains grown during theprevious irradiation step, the length of the grains increases beyond thesingle-pulse lateral growth distance.

In FIG. 3C, the above-described processes of irradiation andsolidification can be repeated indefinitely, leading to grains of anydesired length. FIG. 3C shows the final microstructure which resultsfrom the described process.

FIGS. 4A and 4B show the cross-sectional drawings along the lines I-Iand II-II of FIG. 3C. Here, a silicon layer 42, formed by SLScrystallization technique is superimposed on an insulating layer 41,which is in turn, located on an insulating substrate 40.

According to the SLS technique used herein, the silicon grains proceedby means of lateral grain growth. Thus, the grain boundaries indirectionally solidified materials tend to form perpendicularly to themelt interface. A single pulse grain growth is larger than the thicknessof the amorphous silicon film.

Therefore, the SLS silicon thin film 42, as shown in FIG. 4A, has noboundary in both a first direction 43, i.e., the crystallizing direction(in FIG. 3C), and a second direction 45 which is longitudinal to thesubstrate. The only silicon grain shown in the silicon thin film 43 inFIG. 4A, which is a cross-sectional drawing along the line I-I in FIG.3C.

However, the SLS silicon thin film 42 has a plurality of boundaries in athird direction 44, i.e., the perpendicular direction to the firstdirection 43, the crystallizing direction.

Therefore, a plurality of silicon grains may be shown in the siliconthin film 42 in FIG. 4B, which is a cross-sectional drawing along theline II-II in FIG. 3C.

There is another technique for forming single crystalline silicon on aglass substrate, as disclosed in Korean Patent Application No. 97-18244and its counterpart U.S. application Ser. No. 09/048,321 filed on Mar.26, 1998 and which are incorporated herein by reference. Therefore, itis also possible to fabricate a controller and a CPU circuit built in anLCD by the above-mentioned technique for forming single crystallinesilicon on glass substrates.

FIG. 5 shows an SOP typed LCD according to an embodiment of the presentinvention, wherein the SOP typed LCD includes a pixel arrangement, adriver, a controller and a CPU circuit on a glass substrate.

Referring to FIG. 5, a pixel part, a driver, a controller and a CPUcircuit are defined on an insulated substrate, and predetermined devicesare formed on each defined part. Specifically, a switching device 33-1and a pixel electrode 33-2 which form a pixel cell are formed in thepixel part. A device 32 driving each pixel actively is formed in thedriver. A device 31 which forms a CPU, RAM, ROM, IC, resistors,capacitors, oscillators, connectors and the like is formed in thecontroller and the CPU circuit. FIG. 5 shows only a portion of theforegoing devices.

Each device is fabricated on a glass substrate 30-1, which serves as theinsulated substrate for the same process. Here, each active layer foreach of the devices may be formed with single crystalline orpolycrystalline silicon. In particular, the controller and the CPUcircuit may be made of single crystalline silicon because of thecharacteristic of the devices themselves, while active layers of thedevices of the pixel part may be formed with amorphous silicon, polycrystalline silicon or single crystalline silicone. A technique forforming polycrystalline silicon on a glass substrate is alreadywell-known in the art. Other techniques for forming single crystallinesilicon on glass substrates are being developed and will provide newertechniques in the future that can be used in conjunction with the methodof the present invention.

The process of forming each device is similar to a conventional processof fabricating LCD or semiconductors. However, to form an SOP typed LCD,a new fabrication process for simultaneously forming a pixel part, adriver, a controller and a CPU circuit on a same substrate is proposedin the present invention.

As illustrated in FIG. 5, a first substrate on which a passivation layer35 covering the above-mentioned device lies, is prepared. Correspondingto the first substrate 30-1, a second substrate 30-2 comprising an ITOlayer 37 and a color filter 38 is assembled and placed parallel to thefirst substrate. Liquid crystal 39 is injected between the firstsubstrate 30-1 and the second substrate 30-2. Polarizing plates 32-1 and32-2 are attached to the outsides of the two substrates, respectively.

The above-described embodiment indicates one possible example of thevarious embodiments that can come within the teachings and scope of thepresent invention. Accordingly, the present invention enablesfabrication of TFTs of various types as switching devices for the pixelparts, as well as an overlapped structure or material for LCD panels.

The first substrate of the above-explained SOP typed LCD, as shown inFIG. 6, shows that a pixel array, data and gate driver circuits, acontroller and CPU circuit are preferably formed on a single insulatedsubstrate 40. In the present invention, active layers of the devices ina controller and CPU circuit are preferably formed with singlecrystalline silicon, other active layers of the devices in a driver areformed with single crystalline silicon or polycrystalline silicon, andfurther active layers of the devices in the pixel array may be formedwith at least one of single crystalline, polycrystalline and amorphoussilicon. Namely, the active layers of the driver and the pixel array maybe formed with a non-single crystalline silicon, such asmicrocrystalline silicon.

In this case, as mentioned in the foregoing descriptions, the activelayers of the devices in the driver and the pixel part may be formedwith single crystalline silicon in the same manner of the controller andthe CPU circuit.

The present invention enables fabrication of a pixel part, a driver, acontroller and a CPU circuit on one substrate, whereby the fabricationprocess is simplified and efficient production and manufacture isincreased. Moreover, the present invention makes possible thefabrication of portable LCD products which are significantly reduced inweight and size since the surface area and space occupied by thecontroller and the CPU circuit is minimized.

It will become apparent to those skilled in the art that variousmodifications and variations can be made in a SOP typed liquid crystaldisplay of the present invention without departing from the spirit orscope of the inventions. Thus, it is intended that the present inventioncover the modifications and variations of this invention provided theycome within the scope of the appended claims and equivalents.

1-18. (canceled)
 19. A method of fabricating a system-on-panel typedliquid crystal display comprising: providing a substrate including atleast first, second and third regions; forming a pixel array directly onthe substrate in the first region; depositing and crystallizingamorphous silicon on the substrate to form a driver directly on thesubstrate in the second region; and depositing and crystallizingamorphous silicon on the substrate to form a control unit directly onthe substrate in the third region, wherein the pixel array, driver andcontrol unit are formed simultaneously.
 20. The method according toclaim 19, wherein the the control unit includes an active layer formedof single crystalline silicon.
 21. The method according to claim 19,wherein the pixel array has an active layer formed on single crystallinesilicon.
 22. The method according to claim 19, wherein the driver has anactive layer formed of polycrystalline silicon.
 23. The method accordingto claim 19, wherein the pixel array has an active layer formed ofpolycrystalline silicon.
 24. The method according to claim 19, whereinthe pixel array has an active layer formed of amorphous silicon.
 25. Themethod according to claim 19, wherein the control unit includes acentral processing unit.
 26. The method according to claim 19, whereinthe driver has an active layer formed of single crystalline silicon. 27.A method of fabricating a system-on-panel typed liquid crystal display:providing a substrate including at least first, second and thirdregions; forming a pixel array directly on the substrate in the firstregion; depositing and crystallizing amorphous silicon on the substrateto form a driver directly on the substrate in the second region; anddepositing and crystallizing single crystalline silicon on the substrateto form a control unit directly on the substrate in the third region,wherein the pixel array, driver and control unit are formedsimultaneously.
 28. The method according to claim 27, wherein thecontrol unit includes a central processing unit.
 29. The methodaccording to claim 27, wherein the pixel array has an active layerformed of single crystalline silicon.
 30. The method according to claim27, wherein the driver has an active layer formed of polycrystallinesilicon.
 31. The method according to claim 27, wherein the pixel arrayhas an active layer formed of polycrystalline silicon.
 32. The methodaccording to claim 27, wherein the pixel array has an active layerformed of amorphous silicon.
 33. The method according to claim 29,wherein the driver has an active layer formed of polycrystallinesilicon.
 34. The method according to claim 31, wherein the driver has anactive layer formed of polycrystalline silicon.
 35. The method accordingto claim 32, wherein the driver has an active layer formed ofpolycrystalline silicon.
 36. The method according to claim 32, whereinthe driver has an active layer formed of single crystalline silicon. 37.A method of fabricating a system-on-panel liquid crystal display,comprising: providing a substrate including at least first, second andthird regions; forming a pixel array directly on the substrate at thefirst region, the pixel array having an active layer including amorphoussilicon deposited on the substrate; forming a driver directly on thesubstrate at the second region, the driver having an active layerincluding polysilicon or single crystalline silicon deposited on thesubstrate; and forming a control unit directly on the substrate at thethird region, the control unit having an active layer includingpolysilicon or single crystalline silicon deposited on the substrate,wherein the control unit includes switching devices having at least oneactive layer, wherein the pixel array, driver and control unit areformed simultaneously on the substrate.
 38. The method according toclaim 37, wherein the pixel array active layer further includespolysilicon or single crystalline silicon.
 39. A method of fabricating asystem on panel liquid crystal display comprising: providing a substrateincluding at least first, second and third regions; forming a pixelarray directly on the substrate at the first region, the pixel arrayhaving an active layer including amorphous silicon deposited on thesubstrate; forming a driver directly on the substrate at the secondregion, the driver having an active layer including polysilicon orsingle crystalline silicon deposited on the substrate; and forming acontrol unit directly on the substrate at the third region, wherein thecontrol unit includes switching devices having at least one active layerformed of single crystalline silicon; wherein the pixel array, driverand control unit are formed simultaneously on the substrate.
 40. Themethod according to claim 39, wherein the pixel array active layerfurther includes polysilicon or single crystalline silicon.
 41. Themethod according to claim 19, wherein the substrate includes glass. 42.The method according to claim 27, wherein the substrate includes glass.43. The method according to claim 37, wherein the substrate includesglass.
 44. The method according to claim 39, wherein the substrateincludes glass.